This invention relates generally to radiant, particularly electromagnetic, energy concentration, redirection, and manipulation, and more particularly concerns apparatus and method for employing a transparent means with elements thereof using Total Internal Reflection (T.I.R.), alone or in conjunction with refraction; such elements acting in concert with purely refractive elements (as those in a Fresnel lens) and/or metal mirrors to redirect radiant energy to or from a predetermined zone or zones; such redirection having a predetermined degree of concentration and/or chromatic dispersion. The zones have sources of light, as in photoillumination, or radiant energy receiving means for conversion of the energy to thermal, electric, chemical, or mechanical forms. Alternatively, a further transparent means is employed, with elements thereof having the same design principle (T.I.R.) as above; said further transparent means acting as a secondary radiation redirector for the purpose of magnifying the degree of concentration and/or chromatic dispersion of the radiant energy redirected by the primary transparent means.
The prior art of radiant energy concentration in general consists of two major types, as exemplified by refractive and reflective astronomical telescopes: a refractive lens positioned in front of a receiver, or a retroreflective mirror positioned behind a receiver. The corresponding devices in the prior art of solar energy concentration are the Fresnel lens and the parabolic reflector, which focus solar energy on a target. Furthermore, there are non-focussing reflecting concentrators which have the advantage of fixed daily (non-tracking) position with only seasonal adjustments, but the disadvantage of requiring relatively large reflector areas and delivering only relatively low energy concentrations.
Fresnel lenses are devices using purely refractive elements. However, Fresnel lenses have physically inherent limitations of redirecting radiant energy, due to the low refractive indices of economically available materials, which give high f/ratios and bulky concentrator structure. Moreover, linear Fresnel lenses have, for off-angles in the direction of the grooves, focussing errors, which are also inherent in the laws of refraction, and which limit one-axis tracking configurations to relatively low concentration.
Parabolic reflector concentrators have been used, but are subject to losses of received radiant energy because the receiver is situated between the source and the reflector, which is thereby shaded, preventing in particular the utilization of large heat engines at the focus. Furthermore, the receiver is exposed to environmental degredation and thermal losses, and the inclusion of a protective transparent cover means about the receiver will merely reduce the system's efficiency.
Another reflecting system has appeared in the literature, as reported by Rabl in Solar Energy Vol. 19, No. 5. It employs a retro-reflecting means whose elements have two Totally Internally Reflecting faces, to redirect radiant energy out the same side as it came in. Its only improvement over a metal mirror of the same shape is a potentially higher reflectivity, but the double internal reflection doubles the sensitivity to manufacturing error over that of the present invention.